Art, it is generally agreed, has lost the ability to shock. But visiting the Jake and Dinos Chapman retrospective at Tate Liverpool, I was shocked by both the work itself and the response of many of the people visiting the exhibition.

"Look at what the soldiers are doing," said one parent, holding a toddler up to see. The toddler giggled with gleeful curiosity. I looked around. What the soldiers are doing, countless hundreds of them, is massacring naked civilians and tipping their bodies into mass graves.

"Ooh look, there's more over there," cooed the parent, and the toddler skipped excitedly over to another massacre.

I've always been an agnostic when it comes to the Chapman brothers. But then I'd only ever seen photographs of their work: the deformed children with penises for noses and bodies melded together; the defaced Goya etchings; and the huge tableaux of tiny soldiers. In the flesh, I was struck by the genuinely disturbing nature of their work, the craft with which it is made, the moral anger that informs it. It is as if A Modest Proposal, in which Jonathan Swift darkly suggested the eating of babies to relieve the famine in Ireland, has found a contemporary three-dimensional form. The wit is as savage, the anger at injustice and cruelty as strong.

Far more disturbing, though, was the number of young families visiting the exhibition. Sure, the subject of much of the Chapmans' work is childhood. For one series of paintings, they have imagined themselves inside the head of a GCSE art student. There is an entire room devoted to papier-mache dinosaurs, as well as enough toy soldiers to keep a load of combat-happy kids amused.

And yet, I can't imagine anywhere less appropriate for a small child. If these images were to appear in a film or on television at a time when children might see them, I'm sure these same parents would complain angrily.

Contemporary art, for many years considered "too difficult" for all but the especially educated, has now become a fun day out for all the family. Going down a slide at the Tate Modern is just an extension of the phenomenon that has seen visiting work by Damien Hirst or Tracey Emin become an alternative to a day at Alton Towers.

As the families walked around the Chapman retrospective, sometimes roaring with laughter at the atrocities on display, it struck me that, 50 years ago, this same hunger for the freakish and the mutilated would have been provided by freakshows, or the chambers of horror on Blackpool Pier.

I have to admit to a thought crime. I found my own response to the work - moved, shocked, impressed by its craft - far more appropriate. I'm aware that this is not the right attitude. Artists have more or less given up thinking about what response a work might get. We live in more democratic times, in which the artist just makes the work, and the public make whatever they want of it.

I was about to defend the seriousness of the Chapmans' work. But then it struck me, from the little I have read about them, that they themselves would probably have been amused at seeing their work appropriated as a freakshow. Certainly, the title they have chosen for the retrospective, Bad Art for Bad People, suggests a certain swaggering playfulness, a refusal to take their own work entirely seriously.

And this isn't the first time that work of a distinctly adult nature has been appropriated for the entertainment of children. When the idea of childhood came into being at the beginning of the 19th century, a canon of children's literature was assembled from existing adult work. The Brothers Grimm collected German folktales that were every bit as bloody as the Chapmans' work. Stories such as Snow White found their way into anthologies and eventually Disney movies, becoming sanitised in the process. Even the great savage satirist Swift was recast as a sweet fable for children: Gulliver's Travels may have started life as an adult political satire, but it is now more widely thought of as a children's classic.

If I'm honest, far more children were disturbed by the rats in the Dick Whittington I wrote for the Barbican this Christmas than by the Chapmans' show. At every performance, several children had to be taken out, terrified that the rats were coming to get them. "Kids love being scared," I would say breezily. And I'm pretty sure I was right.

So I should learn to relax. When the Chapman brothers' work comes to London, I plan to see it again, and this time I'll try to follow the dictums of postmodern art appreciation. Art is what you make it. I shall have my response to the work. And other people - even little people aged about seven - will have their response. All of our responses will be equally valid. I just hope I don't get that nagging feeling that, when it comes to works of art, some responses are more equally valid than others.